This application is based on Application No. 396457 filed in Japan on Dec. 27, 2001, the content of which is incorporated hereinto by reference.
The present invention relates to a power supply that is mainly used for driving a motor of an electromotive vehicle such as a hybrid car or an electric car and that is provided with a circuit for detecting a battery temperature.
Power supplies that are used for moving an electromotive vehicle are charged and discharged with a large current to obtain a large output power, and hence the battery temperature may become high during their use. Power supplies that are mounted on vehicles are subjected to a large variation in temperature environment such as a very low temperature in severe winter and a very high temperature in hot summer. Secondary batteries tend deteriorate in performance when used at a very high temperature. When the battery temperature has risen to an abnormally high temperature, further temperature increase can be prevented by stopping charging and discharging or by forcible cooling. For this purpose, power supplies are provided with a temperature detection circuit.
Power supplies provided with a temperature detection circuit are disclosed in JP-A-10-270094 and 2001-52763, for example. In the power supplies that are disclosed in these publications, temperature sensors are fixed to the surface of a battery module. The battery module is a series connection of a plurality of secondary batteries. Temperature sensors are fixed to the surfaces of the respective secondary batteries and are connected to each other in series. The series connection of the temperature sensors is connected to a temperature detection circuit. Each temperature sensor is a device such as the PTC whose electric resistance increases steeply as the battery temperature increases past a setting temperature. Therefore, the electric resistance of the series connection of the temperature sensors increases as the battery temperature increases past the setting temperature. Whether the temperature of the battery module has become higher than the setting temperature can be detected on the basis of the electric resistance of the series connection of the temperature sensors.
In the above power supplies, the series connection of the temperature sensors that are fixed to the respective batteries needs to be connected to the temperature detection circuit by lead wires. Further, it is necessary to control the charging and discharging while detecting the voltage of the battery module. Therefore, in the power supplies of this type, the wiring for the detection of the battery temperature and the wiring for the detection of the battery voltage need to be provided separately. As such, a power supply incorporating a lot of batteries has a disadvantage that such wiring is very complicated. Further, a high voltage may develop across the wiring for detection of the battery voltage. This means a problem that possible short-circuiting in that wiring causes a large current to flow through the batteries, resulting in a dangerous situation.
The present invention has been made in view of the above problems, and an important object of the invention is therefore to provide a power supply capable of simplifying wiring for detection of a battery temperature and a battery voltage.
Another important object of the invention is to provide a power supply capable of increasing the safety by limiting, with temperature sensors, a current that flows when wiring for detection of a battery voltage is short-circuited.
A power supply according to the invention comprises a plurality of secondary batteries, a voltage detection circuit for detecting voltages of the respective secondary batteries or voltages of a plurality of battery modules each of which is a series connection of secondary batteries, and temperature sensors for detecting temperatures of secondary batteries. Each of the temperature sensors has a temperature characteristic that its electric resistance is small when the temperature of an associated secondary battery is low and increases as the temperature of the associated secondary battery increases past a setting temperature. The voltage detection circuit detects the voltages of the respective secondary batteries or the voltages of the respective battery modules as well as battery temperatures by using the temperature sensors as parts of lead wires for detection of the voltages.
The power supply having the above configuration has an advantage that wiring for detection of the battery temperatures and the battery voltages can be simplified. This is because the temperature sensors for detecting the temperatures of secondary batteries are used as parts of lead wires for detection of the voltages of the respective secondary batteries or battery modules and the voltage detection circuit detects the voltages of the respective secondary batteries or battery modules as well as battery temperatures. Since the temperature sensors for detecting the temperatures of secondary batteries are used as parts of lead wires for detection of the voltages, it is not necessary to separately provide wiring for detection of the battery temperatures and wiring for detection of the battery voltages and hence the wiring can be simplified. Therefore, the manufacturing cost of even a power supply incorporating a lot of batteries can be reduced by virtue of simplified wiring. This power supply has another advantage of increased safety. That is, since a current that flows when wiring for detection of a battery voltage is short-circuited can be limited by temperature sensors, a dangerous situation as would otherwise be caused by a large current flowing through the batteries can be prevented effectively.
The voltage detection circuit may detect the battery temperatures on the basis of detection voltages obtained by using the temperature sensors as parts of the lead wires.
The power supply may be such that the plurality of battery modules are arranged parallel with each other, and that a plurality of temperature sensors that are attached to a surface of at least one battery module and connected to each other in series constitute each of temperature detection units that is connected to an associated battery module to serve as a lead wire for detection of a voltage of the associated battery module.
Each of the temperature detection units may be a series connection of a plurality of temperature sensors that are attached to surfaces of two adjoining battery modules that are arranged parallel with each other or a series connection of a plurality of temperature sensors that are attached to a surface of a single battery module.
The power supply may be such that it further comprises bus bars that connect, to each other in series, the battery modules that are arranged parallel with each other, and one end of each of the temperature detection units are connected to the bus bars.
The power supply may be such that it further comprises an absolute temperature detection circuit and absolute temperature sensors that are connected to the absolute temperature detection circuit and attached to surfaces of secondary batteries, and the absolute temperature detection circuit and the absolute temperature sensors detect battery temperatures.
The power supply may be such that a series connection of an absolute temperature sensor and temperature sensors that are attached to a surface of a battery module forms each of second temperature detection units, and that the second temperature detection units are connected to the absolute temperature detection circuit, the temperature detection units are connected to the voltage detection circuit, and both of the absolute temperature detection circuit and the voltage detection circuit detect battery temperatures. Further, the power supply may be such that a temperature detection unit is attached to one of two adjoining battery modules and a second temperature detection unit is attached to the other battery module, whereby temperatures of the two adjoining battery modules are detected.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.